Spacer construction for fluid-insulated transmission lines

ABSTRACT

Improved spacer discs with voltage-control rings are provided to centrally locate the inner high-voltage conductor in fluidinsulated transmission lines. The streamer-control rings reduce the probability of initiation of a streamer across the spacer. Rings, in conjunction with corrugations provided on the surface of the insulating spacers, may additionally be provided for voltage control across the spacers. The spacing between a plurality of voltage-control rings, supported on the spacer, may accommodate the voltage-distribution pattern. The rings may be cast into the spacer as cylinders or cemented thereto, as desired. The rings may be located in somewhat close proximity to both the inner high-voltage conductor, and also to the inner wall of the outer grounded pipe enclosure. Bands of conducting paint, conducting rings of resinous material, such as epoxy, or rings of high-dielectric-constant material may alternatively be employed in place of solid metallic rings.

United States Patent [1 1 Farish SPACER CONSTRUCTION FOR.

FLUID-INSULATED TRANSMISSION LINES [75] Inventor: Owen Farish, Glasgow,Scotland [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: Nov. 14,1972 21 App1.No.:306,492

174/73 R, 73 SC, 142, 140 R, 140 C, 140 H,

140 s,140 CR, 29, 25 o- [56] References Cited UNITED STATES PATENTS3,585,270 6/1971 Trump 174/28 X 3,621,109 11/1971 Nakata 174/28 X3,448,202 6/1969 Whitehead... 174/28 3,328,515 6/1967 Vose 174/140 S3,529,201 9/1970 Rudolph 174/140 R 1,735,560 11/1929 Austin 174/140 C1,513,292 10/1924 Steinberger 174/140 S 2,082,474 6/1937 Van deGraaff.... 174/73 R 3,715,532 2/1973 Morva.. 174/28 FOREIGN PATENTS ORAPPLICATIONS 202,948 7/1956 Australia...., 174/73 R Apr. 2, 1974 17,7613/1913 Great Britain 174/142 Primary ExaminerBernard A. GilheanyAssistant Examiner-A. T. Grimley Attorney, Agent, or Firm-W. R. Crout[57]- ABSTRACT Improved spacer discs with voltage-control rings areprovided to centrally locate the inner high-voltage conductor influid-insulated transmission lines. The streamer-control rings reducethe probability of initiation of a streamer across the spacer. Rings, inconjunction with corrugations provided on the surface ofhigh-dielectric-constant material may alternatively be employed in placeof solid metallic rings.

10 Claims, 1 .4 Drawing Figures ATENTEUAPR 21974 3801.725

SHEET 2 BF 3 FIG.5

MENIEBAPR 2 i974 3; 801.725

1 HIGH DIELECTRIC 4| CONSTANT MATERIAL FIG. I3 XIV-4- 11 SPACERCONSTRUCTION FOR FLUID-INSULATED TRANSMISSION LINES CROSS REFERENCES TORELATED APPLICATIONS Reference may be made to U.S. Pat. applicationfiled Nov. 14, 1972, Ser. No. 306,493 by Alan H. Cookson,

likewise assigned to the assignee of the instant application.

BACKGROUND OF. THE INVENTION 1. Field of the Invention My inventionrelates to electrical-power distribution systems of the type including agas or fluid-insulated transmission line of the metal-enclosed gas orfluidinsulated type consisting of a tubular conductor, with a groundedmetal housing somewhat similar to isolated phase bus, with the exceptionthat the air inside the sealed enclosure is evacuated, and filled with arelatively low pressure high-dielectric-strength gas, such assulfur-hexafluoride (SF gas or other suitable fluid even oil or vacuum,if desired. However, my invention is also adaptable to. variouscompressed gases, or even oil, where this is adesirable medium to use.

The basic elements of such a transmission system include, for example, atubular metallic such as for exam-' ple aluminum inner conductor at linepotential, a tubular metallic enclosure concentric with the innerconductor tube at ground potential, with insulating spacer s, located atspaced intervals along the length of the inner conductor to keep theinner conductor centered within the enclosure. Preferably, anelectronegative gas, such as SF gas, for example, is provided to assurethe proper insulation between the inner high-voltage conductor and .theouter grounded metallic'enclosure.

2. Description of the Prior Art In accordance with prior-art practice,gas insulated distribution systems have been provided for minimizing thedimensions required in overground, or underground electricaltransmission.,Reference may be made to Whitehead U.S. Pat. No. 3,378,731issued Apr. 16, 1968; to Whitehead U.S. Pat. No. 3,391,243, issued July2, 1968; to Whitehead U.S. Pat. No. 3,448,202, issued June 3, 1969; toD. F. Shankle et al. U.S. Pat. No. 3,324,272, issued June 6, 1967, andto Whitehead U.S. Pat. No. 3,331,911, issued July 18, 1967, and, inaddition, to Spindle U.S. Patent 3,345,450, issued October 3, 1967, andUpton, Jr., et a1 U.S. Patent 3,348,001, issued. October 17, 1967, forthe General Field of Application, with which the present invention isconcerned.

Prior-art practice has utilized spacer designs to centrally locate theinner high-voltage conductor concentrically within the outer groundedhousing, or tube.

SUMMARY OF THE INVENTION In accordance with the invention, in one form,there is provided an improved spacer construction in which one or. moremetallic control rings are provided to protect against streamersinitiating from the grounded outer enclosure. Two such metallic ringsmay additionally be provided, one in somewhat closeproximity to theinner wall of the outer grounded enclosure, and the other metallic ringdisposed in somewhat close proximity to the inner high-voltageconductor.

Another form of the invention utilizes a corrugated insulating spacerconstruction having a pair of metallic control rings secured, as bycementing, for example, to the spacer surface.

A further form of the invention utilizes a plurality of streamermetallic control rings spaced apart to correspondwith the voltagedistribution between the inner high-voltage conductor and the outergrounded enclosure. Bands of conducting paint or conducting resinousrings or rings of high-dielectric-constant material may be alternativelyused.

The invention will be more fully understood by reference to thefollowing detailed description, taken in conjunction with theaccompanying drawings, and its scope will be pointed out in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a portion of ahigh-voltage gasinsulated transmission line, together with itstermination point;

FIG. 2 is a sectional view taken through a three-phase gas-insulatedhigh-voltage transmission line, which includes conductors below groundlevel;

FIG. 3 illustrates a commercial-type section of a type sold within theelectrical industry;

FIG. 4 is an enlarged sectional view of a prior-art spacer in whichrings are-painted upon the surface of the spacer, FIG. 10 being asectional view taken substantially along theline x x of FIG. 9;

FIGS. 11 and 12 illustrate still a further modifiedtype of spacerconstruction in which rings made of a conducting epoxy material areutilized in substitution of metallic rings, FIG. 12 being a sectionalview taken substantially along the line XIIXII of FIG. 11; and,

FIGS. 13 and 14 illustrate a further modified-type of construction inwhich relatively high-dielectricconstant bands are cast or otherwisesecured onto the main epoxy spacer, the latter being made of arelatively low-dielectric-constant material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a portion ofa high-voltage gasinsulated system 1, in which the outer groundedmetallic enclosure, or pipe is illustrated and designated by thereference numeral 2. A terminal bushing, or terminator structure 3 isprovided at the end of the pipe 2 to tallic pipes 2, housing innerhigh-voltage conductors 7 maybe used, as illustrated somewhatdiagrammatically in FIG. 2 of the drawings.

FIG. 3 illustrates sections 9 of metal-enclosed gasinsulating systems,each of which comprises an inner high-voltage conductor 7 having agrounded outer metallic housing 2, somewhat similar to isolated phasebus, with the exception that the air within the sealed enclosure isevacuated, and filled with a low-pressure high-dielectric-strength gas,such as sulfur hexafluoride (SF gas, at a pressure say of 22 p.s.i.g.,for example. However, my invention may be used with other fluids, suchas electro-negative gases, or even with oil.

As well known by those skilled in the art, the use of such agas-insulated bus section 9 makes possible a very dramatic reduction inthe'size required by the use of the SF, gas-insulating medium. Forexample, a 138 KV,

1,600-ampere, air-insulated bus 9 has a diameter of 80 inches, whereasthe 345 KV, 3,000-ampere, gas-filled bus requires a diameter of only 18inches. The land area, required for SF gas-insulated siwtching stations,may be'drastically reduced, as set forth in the aforesaid patents setout above.

The bus section 9 may include a tulip-type plug-in female contact 4 anda tulip-type male contact 6, so that many bus sections 9 may beconnected serially together. The outer grounded enclosure tubes 2 may,for example, be welded together, as at eight.

Demand for underground power transmission at higher ratings is everincreasing, as available land for I In compressed-gas insulated cables,or lines 1,one of thecritical factors is the performance of theinsulating spacers 11, illustrated in FIG. 4, which support theinnerhigh-voltage conductor 7. Several studies have been made of theperformance of different designs of spacers 11, and these haveestablished design criteria, which gives the most favorable stressdistribution across the spacer 1 1, so that breakdown will not beinitiated at the spacerterminations under normal conditions. However,contamination, in the form of dust, metallic particles, etc., isregarded as a serious problem in such systems, in that it can triggerbreakdown across the spacer surface 11a. The objective of the presentinvention is to illustrate, as in FIG. 5, the use of concentric metallicrings 13 on the spacer surfaces 11a, which would prevent'the propagationof streamers initiated by contaminants, and thus prevent completebreakdown.

FIG.' 4 illustrates a prior-art spacer design, which is typical forcompressed-gas insulated transmission systems l. The purpose of theshielding electrodes 15, I6 is to improve the voltage stressdistribution at the inside and outside of the spacer l 1. These areintended to reduce the probability of initiation of a streamer; how- 4ever, if a streamer is initiated, say by a free conducting particle ateither electrode, there is nothing to prevent complete propagationacross the spacer surface 11a.

' FIG. 5 illustrates the use of streamer control rings l3,

is reduced to a value dependent upon the ring diameter, and if this isbelow the critical value for streamer propagation, the dischargeterminates at the ring 13 or 14. The metallic ring would be useful inpreventing complete spacer flashover when a particle first initiates adischarge at a spacer 11. However, it is recognized that compressed-gasinsulated systems 1, could not tolerate continuous discharges due tofree conducting particles, because of the effects of discharge productson the insulation of the spacer, and if the particles present were notsuch that they would be destroyed during the discharge (dust, very finemetallic particles), then the system 1 would have to employ other means,such as a particle trap, such as suggested by Trump et al.. US. Pat. No.3,515,939. In the latter case, the metallic streamer control rings 13,14 would still be required to protect the system 1 until the particleswere removed by the Trump trapT (not shown).

In some design of spacers, corrugations 18 are used to improve flashovercharacteristics, In this type of spacer, the corrugations 18 mightprovebeneficial in improving the effectiveness of the metallic control rings14, 14, as it has been found that a fillet of epoxy on the oppositesides of the ring from the streamer improves the performance. FIG. 6illustrates the placement of metallic rings l3, 14 on a corrugatedspacer 20.

The basic system, s uggested in the present invention, is a metallicring 13 or 14 cemented, glued to, or cast into the spacer 11 near one orboth conductors 2, 7.

Variations of this might include the use of a number of rings spaced soas to control the voltage distribution across the spacer 11, such asillustrated in FIGS. 7 and 8, and the use of bands of conducting paintor annular sections of conducting epoxy in place of metallic rings,although possible not as effective as the metallic rings, since they donot reduce the field in the direction of propagation as much as acircular cross-sectional metallic ring-l3, 14'. I f

FIGS. 9 and-"l0 illustrate a modified-type-construction 25 in whichrings 26, 27 are painted upon the surface of the spacer 28. Theconducting rings 26, 27 could be painted onto the spacer surface 28a inconfigurations similar to those utilized previously for the metallicrings l3, 14, 18, 19, 20 and 21. The conducting paint used could be, forexample, a silicone-silver surface coating, such as Eccocoat CC-l0,.manufactured by the Emerson Cuming Company. Or, a silverepoxy paint,such as Eccobond solder 58C, manufactured by the Emerson Cuming Company,could, alternately, be used as a painted conducting ring upon thespacer.

While not as effective as a circular cross-section metal ring, sincethey do not reduce the field in the 'di-.

rection of propagation as much, such painted 'bands would be aninexpensive method for providing additional protection on the spacers28.

FIGS. 11 and 12 illustrate a modified-type of construction 30 in whichthe rings 31, 32 are made of a conducting resinous material, such asepoxy. The metallic rings could be replaced by rings made from ametal-filled epoxy, such as-Stycast I970, manufactured by the EmersonCuming Company, which could be cast onto the epoxy spacer 35.

FIGS. 13 and 14 illustrate still a further modifiedtype of construction40 in which high-dielectricconstant epoxy bands 41, 42 are used. Thespacer 45 would contain bands 41, 42 of high-dielectric-constant epoxy(without metallic filling), cast into the main epoxy spacer 45, whichwill normally be made of relatively low-dielectric-constant material.Such rings 41, 42 would again tend to reduce the electrical stress inthe direction of propagation, and while not as effective as metallicrings, might be preferred for some applica- .tions.

From the foregoing description, it will be apparent that the propagationand initiation of streamers has been controlled by the utilization ofone or more metallic rings 13, 14 which control streamer propagation.

It is to 'be understood that the application of the invention is notrestricted to electrical systems insulated by a high dielectric strengthgas or electronegative gas such as SP The technique could be used in anysystem where there is a spacer mechanically separating highvoltage and.ground electrodes, for example coaxial systems insulated by othergases, such as air, or helium, or by other insulants such as oil or avacuum.

Although there have been illustrated and described specific spacerconstructions utilizing control rings 13, 14, it is to be clearlyunderstood that the same were merely for the purpose of illustration,and that changes and modifications may readily be made therein by thoseskilled in the art, without departing from the spirit and scope of theinvention.

What is claimed is:

1. A high-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer disposed between said electrodes, andatleast one conducting ring disposed on the exposed lateral surface ofsaid spacer and spaced radially away from each of said spacedelectrodes.

2. The combination of claim 1, wherein two concentric conducting ringsare disposed on the exposed lateral surface of said spacer with both ofthe concentric conducting rings spaced radially away from each of saidspaced electrodes.

3, A high-voltage coaxial electrical system comprising a pair of coaxialelectrodes, a disc-like spacer of insulating material separating saidelectrodes, and one or more conducting rings surrounding the centralconductor yet spaced radially away therefrom and supported inside andouter edges of the spacer.

8. A high-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer disposed between said electrodes, andone or more spaced rings painted upon the exposed outer lateral surfaceof the dielectric spacer in concentric relationship with respect to saidspaced electrodes and spaced radially away from both electrodes.

9. A high-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer of resinous material disposed betweensaid electrodes, and one or more rings made ofa conducting epoxymaterial cast into the exposed lateral side of the dielectric epoxyspacer and spaced radially away from said spaced electrodes.

10. A high-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer disposed between said electrodes, andone or more high-dielectric-constant epoxy bands cast onto the mainepoxy spacer, said main epoxy spacer being made of a relativelylow-dielectric-constant material.

1. A high-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer disposed between said electrodes, and atleast one conducting ring disposed on the exposed lateral surface ofsaid spacer and spaced radially away from each of said spacedelectrodes.
 2. The combination of claim 1, wherein two concentricconducting rings are disposed on the exposed lateral surface of saidspacer with both of the concentric conducting rings spaced radially awayfrom each of said spaced electrodes. 3, A high-voltage coaxialelectrical system comprising a pair of coaxial electrodes, a disc-likespacer of insulating material separating said electrodes, and one ormore conducting rings surrounding the central conductor yet spacedradially away therefrom and supported on the lateral exposed surface ofsaid spacer.
 4. The combination of claim 3, wherein two rings areutilized and are in concentric relation.
 5. The combination of claim 1,wherein the dielectric spacers is corrugated.
 6. The combination ofclaim 3, wherein the dielectric spacer is corrugated.
 7. The combinationof claim 1, wherein metallic shielding electrodes are providedperipherally on the inside and outer edges of the spacer.
 8. Ahigh-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer disposed between said electrodes, andone or more spaced rings painted upon the exposed outer lateral surfaceof the dielectric spacer in concentric relationship with respect to saidspaced electrodes and spaced radially away from both electrodes.
 9. Ahigh-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer of resinous material disposed betweensaid electrodes, and one or more rings made of a conducting epoxymaterial cast into the exposed lateral side of the dielectric epoxyspacer and spaced radially away from said spaced electrodes.
 10. Ahigh-voltage electrical system comprising a plurality of spacedelectrodes, a dielectric spacer disposed between said electrodes, andone or more high-dielectric-constant epoxy bands cast onto the mainepoxy spacer, said main epoxy spacer being made of a relativelylow-dielectric-constant material.